The NF-kappaB transcription factor family and the family of IkappaB proteins which regulate the function of these transcription factors are both critical for the defense of the organism: they control the expression of many immunomodulatory proteins as well as proteins which counteract stress. These proteins also regulate the expression of HIV. The overall NF-kappaB and IkappaB activity in a given cell is a result of the expression and activity of the individual family members in that cell. An understanding of the unique functions of the various family members may offer highly specific and limited targets for immunomodulatory therapies. We have initiated a study to dissect the roles of individual members of these two families by generating so-called "knock-out" mice which lack expression of either p52, a subunit of NF-kappaB, or Bcl-3, an IkappaB family member whose physiologic role is largely unknown. To understand the roles of these proteins during immune responses, we challenged these mice with viruses and pathogens. We have demonstrated impaired immune responses in both of these knock-out strains. In the Bcl-3 deficient mice, both antibody responses to influenza and B-cell independent responses to parasites are significantly reduced. We have also generated p50/p52 double knock-out mice; these mice die within several weeks of birth with multiple immune defects. Since the p52 and Bcl-3 genes have been found as partners in recurrent chromosomal translocations in certain B- and T-cell tumors, our studies will be essential to understand the role these proteins can play during tumorigenesis. Individual functions of the NF-kappaB complexes are also being investigated in the context of a given promoter. We discovered that some of the NF-kappaB transcription factors may exert their influence well beyond those genes which harbor known kappaB binding sites in their regulatory regions; the NF-kappaB subunits p65 and c-Rel can interact with the serum response factor (SRF) and thereby strongly and positively affect transcriptional activation through the SRF binding element (SRE) present in the regulatory regions of many inducible genes.